Without limiting the scope of the invention, its background is described in connection with Age-Related Macular Degeneration (AMD). AMD is a progressive disease with a typical onset at the age of 60 years and later. It begins with a loss of central vision (typically in both eyes) and often progresses leading to effectively legal blindness. In the U.S. alone, over 1.6 million persons are afflicted with AMD, with greater than 200,000 new cases occurring yearly. Currently, there is no cure for AMD.
More specifically, AMD patients suffer from a non-correctible loss (a few angular degrees) of central vision (typically consisting of a 6 to 11 degree cone angle). This is the region of vision with the highest resolution that normal-sighted persons use for reading and discerning detail. The eye's perceptive resolution drops precipitously as the angle from the central axis increases.
AMD patients adapt to the loss of central vision by shifting to use their closest-to-center unaffected peripheral vision (e.g., “near” peripheral vision). Peripheral vision typically remains unaffected, but its resolution is significantly lower (even for normal vision persons) so that this region of vision is not useful for any detail acuity, nor can it be rendered useful with any known techniques.
Peripheral vision alone is unable to recover the visual acuity of the lost central vision (the ability to discern fine detail). The most relevant difference between central and peripheral vision of the human eye is the vastly reduced spatial resolution. In theory, an object viewed by the near peripheral vision can be made to appear with as much detail (visual acuity) as by the central vision, as long as adequate optical magnification is applied. Unfortunately, as magnification increases, the useful field of view is proportionally reduced. The resulting amount of scene information that can be perceived by this magnified region is thus also reduced. For example, low vision assistive devices' efficacy is often rated by how much these devices impact reading speed, since reading speed is highly influenced by the number of words presented within the useful visual field (inversely proportional to magnification).
Magnification has been proven to be the single most useful element to help AMD patients. While numerous magnification devices have been introduced in the marketplace, all of them have shortcomings in terms of utility within a single device to assist in a variety of everyday activities (e.g., near and far vision, bright and indoors lighting conditions, etc.) A common complaint from low vision persons is that they cannot simultaneously carry and use multiple assistive devices, each for a particular task, all the time (while remaining ambulatory, performing normal life activities hands-free).